1. Field of the Invention
The invention is concerned with curing photocurable restorative materials such as those used for making dental restorations. The invention also has nondental uses such as the restoration of art objects.
2. Description of the Related Art
Many dental restorative materials are cured by exposure to radiant energy, typically blue light having a wavelength of about 400 to 500 nm. Most such dental restorative materials contain an acrylate or methacrylate binder resin, a filler such as quartz powder or a finely-divided glass (e.g., radiopaque glass), and a photoinitiator. Representative dental restorative materials are described in U.S. Pat. No. 4,503,169 (Randklev), U.S. Pat. No. Re. 32,073 (Randklev), and U.K. Pat. Specification No. 1,544,776.
Because the filler affords limited translucency, photocurable dental restorative materials are desirably laid up in thin layers, typically each having a thickness from about 2 to 3 mm. The layers are successively cured by exposure to radiant energy. Even at a thickness of only 2 mm, the undersurface of the restorative material does not become as well cured as the top surface and central portions, although the difference in the degree of curing may not be great. At a thickness of 3 mm or more, the difference in degree of curing between the top and undersurfaces becomes more significant, and there is a danger that the underside of the restoration might be so undercured as to become a source of microleakage, leading to subsequent caries in adjacent healthy tooth structure. Nevertheless, there is a temptation to make each layer as thick as possible in order to save time and effort, in spite of the hazard of undercuring.
Because teeth fluoresce naturally, dental restorative materials and dental porcelains sometimes contain tiny amounts of fluorescent material to afford a life-like quality. For example, in U.S. Pat. No. 4,514,174 (Dougherty et al.), fluorescent material represents 0.0095% of the restorative of Example 1 and 0.01% of that of Example 2. In U.S. Pat. No. 4,645,455, fluorescent materials are added to porcelains in amounts as high as 6 weight percent.